Using a laser beam to repair defective microelectronic devices is an important technology employed in semiconductor industries, e.g. laser repair of IC chips and laser repair of lithographic photomasks. Typically, a method of laser repair requires two key steps—locating defects precisely and controlling the laser beam to impact only on the places where defects are detected. Simple though these requirements appear, it is often difficult to achieve both.
For example in repairing some electronic or optoelectronic devices, some defects and/or the effect of the defects are not easily identified until the devices are activated. Since laser beam repair devices often operate on wafers to correct identified problems, activating individual devices is not a trivial task. One approach to activating devices involves the use of probes for powering the devices. Probes for testing integrated circuits within a wafer are known in the art. Typically, when used, the probes are positioned to power the device. A defect is detected and the power to the device is terminated. A laser is used to repair the defect. The probes are then positioned again, when necessary, for powering the device and the testing continues. Often the probes form part of an imaging device and the laser forms part of another device. As such, the electronic devices need to be moved between devices. As is evident, it is possible that a single defect will require numerous iterations before being corrected.
Because laser repair involves a process of verifying results of a repair operation, when the repair is performed in a non in-situ manner, repeatedly mounting and dismounting the electronic device is common.
Conventional laser repair of micro electronic devices typically uses nanosecond laser pulses. Nanosecond laser pulses produce problems relating to relatively large heat-affected-zone, melting, and melting related collateral damages. In many applications this deleterious situation can be circumvented, by the accurate positioning of the laser. This results in a known or pre determined heat-affected zone permitting reasonable repair results; For some applications this approach could be particularly more effective and more precisely controlled if a method could be provided to provide feed back in real time during the repair . . . . Unfortunately, such a system does not exist in the known art with nanaosecond lasers.
Another shortcoming of nanosecond lasers when used in repairing electronic devices are plasma effects noticed when the laser acts on plasma formed during heating. Plasma effects can affect conductivity of the material and so forth. Thus, heating the plasma further may result in short circuits at a location proximate the repair or at a location of the repair. A short circuit results in heat dissipation within the electronic device which in turn results in further heating and compounds the collateral damage to the device. It would be advantageous to provide a repair process for repairing electronic and/or opto-electronic devices that is operable while the device is powered.
It is also advantageous to perform in-situ repair such that the result of repair is monitored as it is being performed without dismounting the device.